1. Field of the Invention
The present invention relates to a reloadable optical recording/reproducing apparatus, and, more particularly, to a reloadable optical recording/reproducing apparatus for reloading data continuously from data recorded at the preceding recording operation in accordance with the same modulating rule while eliminating a necessity of creating a gap and/or a preamble portion.
2. Description of the Related Art
Recently, optical cards of a type capable of registering an extremely large quantity of data in comparison with magnetic cards and IC cards have been developed. An optical recording/reproducing apparatus of the type for recording information by using the above-described optical card as the recording medium is arranged in such a manner that information is recorded by changing the reflectance of the medium by irradiating the optical card with laser beams the intensity of which has been modulated.
The optical card has, on the recording surface thereof, a plurality of elongated linear tracks each of which is sectioned into a plurality of sectors which respectively serve as recording units. The sector consists of a preformatted track number portion, a sector number portion, a CRC portion and a data portion on which data can be written. Furthermore, optical cards are usually provided with gaps each of which is formed between sectors in case there is a difference between the bit rate for writing and that for reading. Each of the sectors has, in its leading portion, a preamble portion and a synchronizing portion, while a synchronizing portion and a postamble portion are provided for the terminal portion of the same.
The optical cards structured as described above have been used to exclusively read information or to reload information. When information is reloaded, a gap of a predetermined size is formed continuously from the terminal portion of the sector onto which information has been previously recorded. Then, a preamble and a synchronizing pattern are written before data is written on the data portion. Subsequently, a synchronizing pattern and a postamble are written. However, this arrangement yields a relatively for formatting efficiency because of an excessively large redundancy due to the necessity of providing the gap, the preamble portion and the postamble portion whenever the reloading operation is performed.
Accordingly, a standardized format suggested by the OMCF (Optical Memory Card Forum) is sometimes employed. In accordance with the standardized format, the synchronizing portion is previously formatted continuously from the preamble portion, the synchronizing portion, the track number portion, the sector number portion and the CRC portion. When information is reloaded, synchronization is established by utilizing the synchronizing pattern of the synchronizing portion so as to sequentially write data continuously from the terminal portion of the preceding sector in accordance with the same modulating rule. Then, the track number, the sector number, the CRC and the synchronizing pattern for the ensuing reloading operation are written continuously from the above-described data items. Thus, the writing operation is completed. Then, the synchronizing pattern written at the preceding recording operation is utilized to establish the synchronization at the time of the reloading operation. As a result, data is continuously recorded onto a portion from the terminal portion of the sector, onto which data has been precedently recorded, in accordance with the same modulating rule as that employed at the time of the preceding recording operation.
In the conventional reloadable optical recording/reproducing apparatus of the type arranged in such a manner that information is reloaded onto an optical card onto which information has been recorded in accordance with the thus-arranged format, the portion onto which information has been recorded at the preceding recording operation is read out. Then, a read signal obtained by the above-described reading operation is binary-coded and demodulated before the terminal of the sector is detected from the demodulated data. In accordance with the detected terminal portion of the sector, the modulation of data to be reloaded is commenced. The modulated data is supplied to a laser diode drive circuit which subsequently changes the optical output from the laser diode in accordance with the modulated data so as to write data on the optical card at the same moment at which the terminal portion of the sector has been detected. Consequently, data is written in accordance with the same modulating rule continuously from the portion on which data has been precedently written.
However, in actual fact, a delay of the read signal with respect to the scanning operation performed by the optical head, a delay of the binary digital processing, a delay taken place at the time of the demodulation operation and a delay caused from the filtering processing are generated. As a result, data to be reloaded is delayed with respect to the terminal portion of the sector onto which data has been recorded at the preceding recording operation. In a case where the bit rate at the writing operation is not great, the quantity of the delay of the junction of the sectors is small enough to be followed as a small bit jitter. As a result, the reading operation cannot be substantially influenced. However, in a case where the bit rate is great, the bit interval at the junction of the sectors is enlarged excessively, causing a bit jitter, which cannot be compensated, to be generated. As a result, an undesirable bit deviation takes place. Consequently, for example, a clock bit and a data bit will be read while inverted. Therefore, a critical problem arises in that data cannot be read.